Continuous contact internal rotor for engines



April 3, 1951 I M. F. HILL ET AL 2,547,392

CONTINUOUS CONTACT INTERNAL ROTOR FOR ENGINES Filed April 2, 1946 3Sheets-Sheet 1 VENTOR MYRO .H/LL, FRANCIS .4. H/LL 2nd ATTORNEY April 3,1951 M. F. HILL; ETAL v CONTINUOUS CONTACT INTERNAL ROTOR FOR ENGINESFiled April 2, 1946 RIOR AR 3 Sheets-Sheet 2 INVENTOR MYRO/V HILL,

FRA/VG/SA. H/LL 2nd ATTORNF April 3, 1951 M. F. HILL ET AL commuousCONTACT INTERNAL ROTOR FOR ENGINES s Sheets-Sheet 5 Filed April 2, 1946FIG. ZZZ /2/ INVENTOR MYfPO/V F. H/LL FRANCIS A. HILL 2nd uvg m/ 7.b/uu,

ATTORNEY Patented Apr. 3, 1951 I CONTINUOUS CONTACT INTERNAL ROTOR FORENGINES Myron F. Hill and Francis AT Hill, 2nd, Westport, Conn.

Application April 2, 1946, Serial No. 659,098

18 Claims. (Cl. 103-426) 1 This application is a continuation in part ofour applications Nos. 227,954, filed September 1, 1938, now Patent2,386,896; certain features of application No. 452,654, filed July 28,1942, now

. abandoned; and 561,948, filed November 4, 1944; and contains newmatter not therein shown or described; all constituting a step by stepdevelopment over many years.

It relates generically to rotary fluid toothed displacement rotormechanisms including liquid pumps and motors capableof high pressures,not omitting low pressure gas blowers and motors, and' speclficallyhaving the inner displacement member or pinion rotor as the drivingmember connected to a drive shaft or other device; including also adifference of more than one tooth. It relates. also to ports for suchrotors and driving relations, conforming to special contours of therotor teeth.

These rotor contours are based on new prin- 1 ciples of geometry whichhave escaped the attention of designers of rotors and gears.

They are explained in other cases and herein also with diagrams. Theinvention itself however includes contours and cooperating forms ofme'chanical displacement members producing new results in 2 applicationsto rotary displacement mechanisms J and gearing.

A;series of patents to M. F. Hill, particularly Re-issue Patent No.21,316, described rotors having a diiierence of one in numbers of teeth1 which have continuous contacts or fluidtight engagements forming rotorchambers which open andclose during rotation. As they rotate, actingas'a, pump for example, each tooth of one rotor enters and leaves allthe tooth spaces of the other rotorf driving out their fluid contentsand sucking in more. Each tooth slides or rolls over all the ,teth ofthe other rotor, providing a hunting relation (interchange of toothengagements) between them all. such precision that this contactpersiststhruout rotation. They have tight fits between all the teeth,and as pumps and hydraulic motors have been contributors to swift andprecision operation of tanks, planes, ships and amphibians in warservice. Also as lubricating pumps in autos and boats. Their highefficiency as lubricating pumps for engines and superchargers in planesprovided flight at high altitudes. Across the open mesh region the toothcrowns of one rotor slide over the tooth crowns of the other rotor. Withusual moderate oil pressures it is a pressure-less contact.

An open crescent space across open mesh between teeth out of contact,where notooth con- The rotors are made with I back lash betweentheteeth, between teeth performing no useful pressure function. Contactsbetween teeth of opening chambers and teeth of closing chambers at thesame time cannot take place with back lash. The difference of two (ormore) in the numbers of teeth, such numbers having no common divisor,provides abasic fractional ratio having a dilierence of one which isessential for maintaining continuous travelling engagements between theteeth, and to generating the rotor curves accurately at a singlesetting.

Such rotor contours require specially designed ports. The difficultresettings in manufacturing rotors tacts occur and prevent contacthaving even numbers of teeth are eliminated, as

well as their hammering and uneven wear.

Back lash between our rotor teeth of continuous contact acquires a newfunction. Shaft bearings with enough looseness to run, let the teeth ofone rotor ride on the other under high internal fluid pressures, tendingto heat the rotors to the point of binding. Back lash and the crescentspace at open mesh prevent it.

These traveling engagements and contacts, in

operation, lap themselves to a fit that is evident upon inspection ofteeth in service. A polish occurs upon contacting surfaces. It may beobserved that a mostly rolling contact occurs at iullmesh where theteeth of one rotor drive the teeth of the other, and between the toothsurfaces in contact along a port, where a rub occurs. If withmanufacturing or mass production tolerances, some teeth fail to makeactual contact, the rub elsewhere wears oiT the tooth surfaces untilthey all engage. Nevertheless, when first made they are to be in suchproximity as to have driving and'pressure'holding engage merits capableof running themselves in, in

service. Departure from the Gerotor method of designing rotor contoursmakes possible the hunting relation between all the teeth of the rotors,larger displacement and improved pressure angles in the driving rangebetween the teeth at full mesh.

I The crescent space, which requires no metal or other insert to sealthe ports from each other as in other fluid mechanisms; also helps toprevent the pinion from contacting and. riding on the teeth of the"outer rotor from one end of the crescent to. the other. This crescentspace is as the area at open mesh between two circles, one

passing thru the tips of the pinion teeth and the other thru the tips ofthe teeth of the outer rotor.

Back lash was old, but combined with the con,-

tinuous contacts, it prevents the teeth of the pinion from riding on theteeth of the outer rotor where no fluid pressure holding engagements areneeded, between full mesh and one end of the crescent space leaving thecontinuous contacts and engagements between the other end of thecrescent space and full mesh unafiected. A difference of two or moreteeth between rotors or gears, old in themselves, performed unexpectedresults with continuous contact rotors, causing the rule of continuouscontact to be modified, first to include multiples of the ratio having adifference of one; and then modified again to include the huntingrelation which solved a manufacturing problem.

It also permitted rotor teeth to'be' built loose, with the contactsbrought into action by driving, whether by a shaft or by fluid pressure.Thus rotors may lap themselves to a perfect fit in service to providerotor chambers sealed at both ends, and to provide interchangeable andor reversible high and low pressure ports for pumps and motors foroperation in opposite directions. The terms high and low merelydifferentiate between the ports. I

These step by step developments, each valuable in itself, produce newresults in continuous contact rotors. I x

The first difference of twoteeth appeared when, inspecting Fig. IX ofthe reissue patent to M. F. Hill, No. 2l,3l6, the tooth spaces of thepinion appeared wide enough to hold another tooth, and the outer teethwide enough for another tooth space. This doubled the number of teethand they acquired a difference of two which provided the much neededcrescent space to eliminatethe riding of one rotor on the teeth of theother at open mesh, without loss of the continuous contacts. See alsoPatent No. 2,386,- 896, Fig. XVI having even numbers of teeth. Useful inreduction gearing this idea was patented in patents, Nos. 2,091,317 and2,209,202, to F. Hill. The disclosure in these patents was limited tomultiples of rotor teeth having a. diiference of one for gears. Thecontours and pressure angles of the Reissue Patent 21,3'1'6characterized the teeth. Furthermore, in multiplying the teeth, a partof the tooth height was sacrificed; and whatever was done to themthereafter, such as reducing the numbers of teeth again while increasingthe eccentricity, the lost height still prevailed. The height of a toothaffects the size of rotor chambers between the teeth,- and so limits thedisplacement as compared with our later form. Incidentally the centersof the master curvesfor two sides of each tooth were doubled in number,and were evenly indexed with each other. The multip-led gear teeth hadthe same type of contours near the convex tops or crowns that theoriginal rotors had.

The gear patents disclosed no pump casing or ports. V I

When teeth are multipled, even tho they had a hunting relation betweenthem, the hunting relation between all the teeth is lost.

In our Patent #2,386,896 the off sides of adjoining teeth of the outerrotor are limited to a common center, and a similar relation existsbetween the near sides of alternate pinion teeth. Our present rotorshave no such limitation.

Rotors having a difierence of two teeth, resultin from multiplyingsmaller ratios of integers differing by one, do not have the huntingrelation so essential to easy manufacture and good service. To index twosets of teeth with relation to each other with the exactness needed forefiicient fluidtight high pressure relations, if not impossible is atleast a great expense, and in mass production is difiiicult to maintain.In generation, one set of teeth is first generated on a blank. The blankmust then be indexed exactly half way, and the second set generated. An

error in indexing results in hammering of teeth,

noise, lost efficiency and wear. The usual manufacturing tolerance wouldruin rotors for efficient service. With a full hunting relation there isno second indexing, and the exact indexing char"- acteristic ofgeneration of all the teeth is aocom plished. The hunting relationenables each tooth to engage in proper turn all the teeth of the otherrotor. This evens up any possible wear due to diiferences in hardness ordurability of teeth, or grit, and maintains a smooth operatingmechanism. I

Realizing this, another tooth was added to each rotor, changing theratio circles accordingly, and it was discovered to be possible. It wasa departure from simple multipling, and eliminated the difiicult secondindexing. Removing a tooth has the same effect. 8 x 10 rotors might bealtered to 7 x 9 or g x 11 for example.

Then came another conception, a more scientific method of designingrotor contours for continuous cont-act, particularly useful for rotorshaving any difference in numbers of teeth greater than one. A diiferenceof two increased the height of a rotor tooth, and added displacement. Itmade possible a better location or inclination of the sides of rotorteeth to get better pressure angles. It made possible the location ofdriving surfaces across the ratio circles instead of mostly outside ofthem, thus reducing angular slip. It made possible the more intelligentlayingout of rotor teeth, selecting the best radii of curvature, anddetermining the circroidal addition more accurately than with thegenerator machine. Mathematical calculations are possible; but are mostintricate and take much time. But in a graph, comparison of diiferentcurves is easy. It is regarded as the final step in adapting this newtype of rotors for commercial development.

I In new geometrical relations rules or laws are sought to guide thosewho are to become skilled in the art. The first rule that appearedimportant, was that in gears, one within the other, there must be adifference of one tooth only, since a tooth of one had to travelcontinuously over all the teeth of the other and the speed ra= tio hadto be the ratio of the teeth. This was accepted for many years by thosedeveloping and commercializing this art. The initial patents, to M. F.Hill contained claims limited to the differ ence of one tooth. I

Whenit was discovered that the teeth of a ratio differing by one couldbe doubled, to make a difference of two, or trebled to make a difierenceof three, the rule had to be modnfied, and extended to include themultiples.

Then finally it was discovered that it was not the ratios of teeth thatwere controlling but the basic ratios themselves which must have adinerence of one, even with ratios of fractional numbers.

and finally also it appeared that the hunting relation between all theteeth was possible only for teeth based either on integers having adiff'e'r'ence of one as in the original rotors orona fractional ratio,having a difference of one, the

t actual number of teeth being found by multiplying the ratio numbers bythe denominator of their fractions. Merely multiplying teeth of rotorslost the hunting relation between all the teeth.

The lowest ratio having a good driving relation between the rotors maybe 2% to 3 the rotors having five and seven teeth. They are not.multiples of any ratio having lesser numbers of teeth, and have greaterdisplacement than four to five teeth of the same outside diameter.

A 1 /2 x 2 ratio, with 3 X 5 teeth is possible for low pressures tho thedrive action is poor. A x 1 /2 ratio, having 1 x 3.teeth might requireadditional driving gears to keep them in registration. Multiples of verylow ratios, 1 x 2 or2 x-3 doubled or trebled may fit some needs; allhaving the continuous tooth engagements.

With the pinion drive so called, a pinion is freely mounted on a driveshaft and key to find its own best running position, between the sidewalls while driving the outer rotor. Rotors as is well known, rotaterelatively at speeds according to their tooth ratio. That is, speeds aredetermined by their relativenumbers of teeth. A 5 tooth pinion indriving a seven tooth outer rotor or displacement member, rotates fasterthan the seven tooth member. It rotates seven time to five turns of theouter rotor. Their rotor speeds therefore are, inversely proportional totheir numbers of teeth. p

The five to seven tooth rotors have such radiallydeep rotorchambers'however that they leave little room for a shaft hole of a sizeneeded for h igh pressure operation; so that then teeth of the pinionrotor are made integral with the shaft. Additional elements are requiredfor endwise freedom; such as an Oldham clutch at the driving end'of theshaft. With seven to nine teeth or more (a ratio of 3 to l thereis ampleroom for a shaft hole for a high pressure shaftfwith the pinion rotorfreely mounted and keyed to permit it to find its own best runningposition between side walls. 7

As these rotors rotate at ratio speeds wtih relation to each other, thatis at speeds proportional to their numbers of teeth, directly orinversely, the new contours make continuous contacts and engagementswith each other.

A difference in the numbers of teeth of a tooth ratio is not a matter ofdegree for another. reason." In rotors of the same size, a difierence oftwo gteeth increases displacement while a diiierence of three teethreduces it, because of the longer; crescent space in the latter andfewer rotor chambers at any one instant to pump with. If tooth ratioshave a common divisor, instead of beingindivisible by any commondivisor, they require shifting the reiative settings of tool and rotorbetween generation of sets of tooth contours, introducing extra work,inaccuracies, noisy operation and more wear, so that the difierence isfar reaching.

' With difierent numbers of teeth, critical intersections of certainnormals to certain curves have different relative positions in thegeometry of the Hill Theorem to be discussed later.

Rotors have bearings for the pinion shaft in side walls inside of portswhich are often located in sidewalls, providing larger port access toro-- tor chambers than radial ports. Seven to nine teeth allow ampleroom even for antifrictionbearings inside of the ports. These and manyother factors difierentiate the various types and ratios of teeth.

The next stumbling block. encountered in the development of rotors withcrescent spaces and back lash was port relations. As already notedrotors having a difiference of one tooth, and having no crescent space,had continuous contacts between all the teeth. Ports areseparated byabutm'ents, that is, areas in the enclosing walls between the ports toshut off escape, of liquid from one port to the other. It is thepractice to make the abutments of such length that one rotor chamber isnot disconnected froma port until it has connected to the other,directly or thru the crescent space, to avoid liquid look. It is calledthe overlap. But the ports are separated substantially by a toothengagement that prevents dissipation of pressure. Now the crescent spaceshortens the'intake port of a liquid pump. The intake volume isincreased by-the greater eccentricity (that of 3 inch 6 x '7 rotors iswhile that of 5 x 'Z, same'outs'ide diameter, rotors is the volumeincreasing with the ra tio and its eccentricity). 'Eadially deeper portscompensate, lying outside and inside of the path of tooth. engagement.

If in doubling the numbers of teeth in a liquid pump two fluidtightengagements occur between closing chambers disconnected from crescent orport areas, liquid lock ensues .and stoppage" of rotation. Increasingthe difierence in the numbers of teeth therefore requires modificationof port relations relative to the tooth contours.

With back lash between the teeth of a pump only one end of the crestcentspace may be separated from a tooth chamber containing high liquidpressure by a fluidtight tooth engagement. The separation may take placeat one end of the crescent only and that end depends on the kind ofrotor drive applied, whether fluid or mechanical, and the direction ofrotation.

Enough back lash to prevent the teeth on both sides of one .rotor fromriding on the teeth of the other opens a crevice between the teeth whichin the sizes shown, would'dissipate pressure, un'-' less otherwiseprevented. The end of the path of contact occurs when the crevice startsto open. The location of a fiuidtight engagement overa range from onetooth to the next is afiected by the ending of the path of continuousengagement. In our present invention a fiuidtight contact or toothengagement occurs in the full mesh region and prevents the escape offluid between the teeth from one port to the other.

Paths of continuous engagement vary in different types of continuousengagement rotors. There are hosts of types all based upon thegeometrical principle of the circroidal addition. There are three typesof tooth ratios and variations of them. In the well known Gerotor" typeof the prior art, having a difference of one tooth;

all of the teeth are tightly fitted to each other. The outer rotor has acircular curve on each tooth extending over the top and sides with acommon center, all the tooth centers being evenly indexed. The secondtype is that shown in the gear Patents Nos. 2,091,317 etc. The outerteeth have the same side arcs of circles, but no completelypconvexcrowns, and the arc centers are evenly indeXed. The third type, in thiscase, has teeth differing by two or more with a full hunting relation,preferably with a center of the arc on one side of each outer rotortooth unevenly spaced between all the centers of the arcs on the othersides of the teeth, affording larger radii better pressure angles andgreater displacement.

The paths of tooth engagements difier in these types. In the first orGerotor form, the path is continuous around the teeth, with a :loop atfull mesh, '(Fig. .XXI) of prior ,art. Without back lash in the secondand third'type the path starts from the end of a crescent space andstops at full mesh. Another path .is the :reverse on the other side ofthe rotors. The third form is complicated 'further'by-the odd'ratiobased on fractional numbers having a difference of one,xwhich has thehunting relation. The location of the fluid tight tooth engagement, orits range from one tooth to the next, is :affected'by these dinerences.With back lash between the teeth, one of the paths of contact in thesecond and third types, is removed.

Pressure angles between the teeth in the driving range have an importantefiect upon the internal resistance of a fluid mechanism and the powerrequired to drive it. The pressure angles in the six and seven toothrotors of the prior art, having a difference of one tooth, usedas'motors, are prevented from rotating by heavy fiuidpressure thrustingthe outer rotor away from its axis, and thrusting the teeth at open meshagainst each other. In the gear patents the tooth contours (andpressure-angles at full mesh) were the same as in Gerotors. Pressureangles between our 'Rotoid teeth making continuous contacts are notfixed as in gearing of the-present day. The pressure angles vary as onetooth rolls against the other across full mesh. The angles of the six toseven tooth Gerotors were of the order of 30 to 50, while in Rotcidshaving five and seven teeth the angles are nearer 9 to 17. The radii ofcurvature may be increased, and the driving curves more steeplyinclined. ,Also they may now be located wherever desired, inside, acrossor outside of the ratio circles, aways obeying the 116- quirements ofthe circroidal addition. Low pressure angles and fluid'pressure balances,favor operation as a motor. The constructionprovides bearings favoringstarting as a motor, and favoring metering. The low pressure angles alsoprovideleast friction between the teeth,.so that fluid pressures neededfor operation are low. :As a meterthe difierence between inflow andoutflow pressures is slight, favoringgreater accuracy. As a motor,particularly for hydraulic operatiomeficiencyishigh.

.One of the factors of lowinternal resistance is the character of thetooth engagementin the driving range at full mesh. .In .X '7,toothrotors it is :within a few .per cent of va pure ;roll of a curvexcurve on a concave curve having slightly larger radii-of curvature.

Continuous .contact rotors are now usually manufactured by breaching theouter rotor and regenerating the pinion. The broach has circular cuttingedges to cut thecircular arcs on the outer rotor teeth. The bottoms ofthe tooth spaces .do not have to ihave aigenera-ted form as long as theyclear'the tops of the pinion teeth during rotation. They-are usedmainlyfor liquid mechanisms. For air or other gas the bottoms of theitooth'spaccsmay be closer to the-tops of the piston teeth and even-havethe same form, making allowance in the bottoms of the tooth spaces-forthe escape of liquid in the tooth spaces acrossjfull mesh. For partofthe distance across full mesh this liquidmay assist or act as asubstitute for tooth contact,-and thus partake of the character ofafluid pressure holding engagement.

The pinion is generated by means of a tool, be it a miliing cutter or:grinding wheel, .whiclrhas the rshape of ;a tooth f the outerrotor, thatis, 1

the circular arc. The larger the curve of this tooth is, the larger thetool and'thc faster itsoperation. The relative size shown in (Figs. I-IIJ was selected as a mean between extreme sizes each of which in thatform has a disadvantage, in reducing displacement.

Fluid displacement mechanisms are apt to be taken 'for granted. In gearfluid mechanisms havingno continuous contacts, liquid locking andjamming are not critical factors. But in fluid mechanisms havingcontinuous tooth engage,v

ments, the exact location of ports as to tooth contours, .or criticalportions of them, are so important that wrong locations of them resulteither in liquid looking or loss of efficiency thru leakage. In Gerotormechanisms having a difference of one tooth, the rotors whenmanufactured areso tight that pressure is used toput them together. Theyare rotated slowly at;first, and as the lap themselves to a running fitduring rotation, they are enabled to run faster and faster. The powerfor rotating them, high at first, steadily reduces until when completelylapped to each other, they may be run at high speeds without generatingheat, provided .fiuid pressures are not too high.

In thenew rotors, having the crescent and back lash, the pinion can dropthru the outer rotor withouttouching it.

With crescents and back lash there are inhibitions to avoid port lossesor liquid locks, involving an end of a path of tooth engagement. Theoverlap of the ends of ports, where a rotor chamber connects with oneport before it leaves the other, is not critical at open meshinGerotors. In the new rotors with back lash it is atan end of thecrescent. It has to beat the properend, otherwise the port losses injurethe utility of the pumpor other fluid mechanism. That end is determinedby the drive direction, also the direction of the drive. It is the drivethatbrings the teeth together to form a fluid pressure holdingengagement. Without it' fluid can flow thru chambers having no fluidpressure holding engagements.

:Our rotors and ports have-difierent uses.

One may be with the pinion driving the outer rotor, clockwise. Oneabutment at full mesh and one at the right hand end of the crescentspace arein action aided by passingtooth contacts to bar escape ofpressure fluids back into the suctionport. The abutment at the left handend of the crescent space area does not bar pressure from the dischargeport irom being communicated to the crescent area thru the crevicesbetween the teeth due to back lash, so thatthe crescent area has thesame fluid pressure asthe ischarge port.

Another use be with the pinion driving the outer rotor anti-clockwisewhich reverses the operation of abutments and ports. At full mesh thecontacts maintained tight by the driving action are passing the abutmentin the opposite direction to that above noted. The left hand crescentabutment with tooth engagements kept tight by the driving action passingover it, bars the escape of fluid pressure from the crescent areabackinto the intake port along which the rotor chambers are opening.

When two abutments are used, one at each end of the crescent area, oneis out of action due to back lash and the other has the overlap. This isthe reversible construction. Back lash and overlap are, modified forsuccessful useas. motors.

The different operations as motor and pump,

and their directions of travel involve tight tooth continuous contactson the one hand and'back lash with free leakage on the other hand. Ifthe shaft drives the pinion in a pump, the contacts between the teeth tokeep the chambers sealed from each other occur where the chambers areopening, and the chambers that are closing are connected thru back lash.to the crescent space, which is sealed off from the opening chambers andintake portby an abutment area, and the tight tooth contacts. a a As ahydraulic motoigthe reverse is true, the closing chambers being sealedfrom each other and from the crescent space. The latter is thenconnected tothe opening chambers thru back lash. v

" In thedrawings:

Fig. I is a sectional elevation of the liquid pump or-motor constructionon line- I -I, Fig. II, the rotors being indicated in broken lines, fulllines being shown in Fig. IV. iFi'g. II is asection of Fig. I on line11-11.

6 Fig. IIIis an elevation of the left side of Fig. II omitting the boss,seal'members, shaft and thrust plate. l r

- Fig. IV is to indicate tooth-relations between the rotorsJ 4 Fig. Vshows rotor members and ports tocooperate'with them for a one-directionpump or motor.

Fig. VI shows the rotors in another position indicating portmodifications at full mesh.

Fig. VII shows the parts of an Oldham clutch for driving the shaftavoiding end thrust on the rotor teeth.

Fig. VIII showsrotors of the prior art having a difference of one tooth,with the teeth doubled in number, resulting in 8 and 10 teeth, and theirpaths of contact.

"*FigrIX shows rotors having the same tooth forms and the same eccentricrelations, with the teeth reduced in number to 5 and 7.

Fig. X shows a modification of the teeth of the rotors in Fig. IX.

' Fig. XI shows'rotors having 9 and 11 teeth built from the same type ofcurves.

Fig. XII shows a diagram of a more scientific method of designing rotorcontours.

Fig. XIII shows a diagram of ratio circles and circroids upon which Fig.XII is based.

Fig. XIV shows a detail of the balancing duct system.

Fig. XV shows another detail in a different position.

Fig. XVI shows the ducts upon the side of the casing with the seal capremoved.

Fig. XVII is a vertical section of a modified form of fluid mechanism onthe line XVII-XVII in Fig. XVIII.

Fig. XVIII is a right hand elevation of Fig. XVII with the coverremoved. Fig. XIX shows a spring to keep the seal inFig.

XVII tight.

I Fig. XX is an enlargementof the seal in Fig.

XVII.

g-Fig. XXI illustrates a form of rotors of the prior art now on themarket. I The figures in the drawings illustrate the adap versibleliquid pumps and motors, the useful in other fluid mechanisms. Lowpressure gas may be pumped without much loss of power in fluidmechanisms adapted to handle liquids.

Rotors are shown in a series of positions to" illustrate the portrelations necessary for such rotors having contours providing continuousfluid pressure holding engagements between the teeth. I .7

Two typical units are shown, onerequiring that the teeth of the pinionbe integral'with a driving shaft,'and others having the pinion keyed tothe driving shaft. The former has the small est size with relation'tovolume of displacement. while the latter has greater pressure holdingcapacity. 1 1

Ports and continuous contacts leakage of fluids between the teeth, arethe types of contours used. and the port forms necessary for providinginlets and outlets for fluidwithout looking or jamming on the one handor copious leakage on the other. Copious leakage of the prior artrequires larger pumps and more horsepowerto operate them, and are at adisadvantage in competition;

i In Fig. I the casing member 12 is shown in section, with ports l3 andI 4, in this case, either one of which may be the inlet and the otherthe outlet. f -In {other words this is a reversible mechanism.='v pFluid displacement (rotor) members are indicated in broken lines 15 andas, and in various positions in Figs. IV, V, and VI. Inorder to designports, firstthe path of contact i'i between the teeth has to bedetermined Fig. IV shows this path of contact 6! and path of toothcontact or engagement Ila on the other sides of the centerline CL (whichpasses thru the two rotor axes, ac and p0).

Diiferentrotor contours have correspondingly difierent paths of toothengagements. The con tour of a pinion is determined by generating it,using as a generating tool a cutter or grinding wheelhaving the form andsize of a dominating convex master curve of a tooth Q8 of the'outerrotormember '2, this tool being caused to cut or otherwise shape .theteeth of the pinion, while the pinion blank. rotates on its own axis 1/.and

ing the fifth; then skipping the first, forming the second, skipping thethird and forming the fourth when the .rotor is completed. This unusualgenerating process results from unusual tooth ratios and their ratiocircles. j. The; five and seven tooth rotors have a ratio which-dif"fers by one, this difference being a necessity for continuous contactrotor teeth contours. The ratiois not between integers but betweenfractional numbers, in this case, 2 and But discharge of fluid, isindicated at 2i.

since rotors cant run with a half tooth, these numbers are multiplied bythe denominator of the fraction, that is by 2, providing the numbers ofteeth of and 7. If the fractional ratio was 2 and 3 /2,, the toothnumbers would be 9 and 13, the ratio numbers being multiplied thedenominator 4. These fractional ratios have what is called a huntingrelation by which each toothof one rotor in some order, makesengagement, a travelling engagement, with every tooth of the otherrotor. That makes it possible for a tool representing one tooth of onerotor to out every tooth of the other rotor. When the tooth forms of onerotor are selected or form-ed arbitrarily, the bottoms of narrow toothspaces may be of minor importance, particularly on the outer rotor, andas long as they keep out of contact with the tops of the teethf theother rotor. The depth or form of the bottom of the is unimportant, sofar as continuous engagement is concerned. For use with liquids deepenedtooth spaces in. the places described, work well, and in fact mayprovide easier inlet and outlet of liquid from the chambers between. therotor teeth nearing full mesh. Reference is made to the reissue patentto Myron Hill, 21,316, for further description of the generating processand. to the patent to Hugo Bilgram and M. Hill, 'No. 1,798,659describing a suitable gen.- erator. For these contours the mill orgrinding wheel travels across the rotor blank, in. a direction parallelto the rotor axes; accomplished by mounting the Bilgram Hill machineupon a shaper, which may provide the cutting tool, or which may carry agrinding head.

Other ratios may be provided, such as 3 and 4 4 and 5 /2; etc, or 3 /4and 4 /4; or any other fractional ratio differing by one. Only thesefractional ratios have the. desired hunting relation. Other ratios basedon integers, such as 4L and 6, 6 and 8, and the like, for many purposesmay be useful. and novel combinations with ports and novel features ofthe rotors and mechanisms, aside from the hunting relation, lie withinthe scope oi our invention.

The path of contact between rotor contours varies with the type ofcontours used; with the ratio, whether of even or odd fractionalnumbers; and with the presence or absence of back lash. Fig. XXI shows atype of rotors now on the market, and the path of tooth engagement 24.This path 24 is endless and has a loop 24s at full mesh. Similar rotorswith teeth doubled in number are shown in Fig. VIII. One path of contactis shown from 59 to its and another from 26a to 29. If an abutmentshould be shifted somewhat, angularly (to right or left), it would havelittle effect.

In Fig. I the abutment at full mesh performs a similar service, beinglocated between the ends 4'! and 48 of the two ports i3 and M- In a onedirection pump as in Fig. VI the ends of the ports 35 and Ma may beextended into this abutment area as indicated at 32 and 4 3 for veryclose fits of rotors between their side walls, or for large pumps ormotors, a motor being more or less a reverse of a pump. If back lash isapplied to these rotors, one of the paths is eliminated and the portshave to be accommodated to the single path of tooth engagements.Deepening the tooth spaces of the outer rotor slightly, provides easierRemoving three teeth'from each' rotor produces a ratio of 5 X '7 shownin Fig. IX, the basic ratio being 2 x 3% which has the difference of oneneeded for continuous tooth contacts. These long tooth divisionscomplicate the port problem, particularly inv View of the crescent spaceat open mesh, The" radial increase in the heights of teeth in Fig. Xincreases displacement and provides for radially large port areas. InFig. X the. sides of the pinion teeth. shown in Fig. IX are broughtcloser together.

The ports for'the different types of rotor operation vary, the ports forone type often not working with another type, sometimesbeing'inoperative and. sometimes being subject to the evil of all liquidpumps, cavitation, with its attendant hammering, noise and vibration.While this application is primarily concerned with liquid pumps andmotors, it is also concerned in a generic way with any kind of. fluidmechanism where the invention can be of service.

A drive. shaft may be. either the shaft; that drives a. pump rotor orthat. is driven by the rotors acting as a hydraulic motor;

In Fig. I ports. were shown. for a reversible operation and they differ.from. the; ports in Figs. V and VI because the latter two are notdesigned to be reversible. They are alternative: as to Fig. IV. Any typewith. its ports. may be used in Figs. I and II.. The port conditions atfull mesh and at the two ends. of. the crescent are. the. factors thathave to be dealt with. Another factor that has to be dealt with is thepath of continuous tooth contact and whether, with back lash between theteeth, it is a single'path on one side of the center line (with its bookat f-ull mesh), or, without back lash, paths on both sides of the centerline. In those forms of rotors proposed heretofore, such as the patentto Feuerheerd in which the contours made accurately are inoperative. In.commercial pumps the'teeth have loose relations, and port relations arenot exacting, since fairly free leakage between the teeth elimihatesthe. possibility of jamming of; liquid and liquid look, so that. it ismerely a question of. lost displacement and of higher powerrequirements. Such mechanisms are incapable of efficient service.vViking and Tuthill pumps have no suchcontinuous tooth contacts and theirports are separated at open mesh by crescent inserts, over which theteeth of both rotors travel out of contact.

Hydraulic motor, pinion drive Operating anticlockwise, and illustratingwith Fig. I, high pressure (as distinguished from low pressure) entersthru the port !3. This pressure fluid should not escape into the outletport 14 except thru opening chambers as they pass the abutment 34a. Theends of the abutment if modified as at 40, let a slight amount of liquidescape but pressure liquid opens the rotor chambers causing rotation,minimizing the escape of liquid. A rotor chamber in the position of 46in Fig. VI has not passed the critical point 29 (inboth figures) and socontains low pressure liquid. As the chamber leaves the low pressureport M (Ma in Fig. VI) it connects with the high pressure port I3 (35 inFig. VI). If it connects before reaching full mesh, and is disconnectedfrom the port l4, it would have to try to compress liquid, and in theeffort become liquid locked. So that the chamberconnects with the highpressure port I3 after it has stopped closing at full mesh. The portextension 32 in Fig. VI freely connecting with the chamber across fullmesh favors this relation, but is not useful in reversible motors.

In Fig. I the ports inside of the paths-of contact i! and Ha may extendcloser to the full mesh point than those portions outside of the pathsof contact. The extension 44 extends to the chamber at full mesh and itslimit 48 corresponds to the limit of the extension 44 in Fig.

VI. If these ends do not quite connect with the and is still closing, itmust have another outlet 1 a to avoid liquid lock. Therefore the point28 is located by the length of the chamber at full mesh, since that iswhere closing has ceased. The left end of the chamber theoretically hasreached the point 29. In practice an overlap is needed t9preventlmomentary jamming in the chamber, be

iore it disconnects from the port 4 la which must have made connectionwith the port 35 containing the high pressure liquid that operates themotor.

to open and thereafter is oadsed to continue to open until its left orforward end has passed the abutment area near the crescent space. Acorresponding overlap at this abutment remedies cavitation noises.

All that an overlap needs is that the theoretical boundary of a port becut away slightly. It makes the abutment smaller in effective area thanthe chamber. high pressure port 35 to the low pressure port 41a. Withthe narrow spaces between the rotor teeth andthe inertia and momentum ofoil flying by at high speed, the loss of volume is negligible. But itsoftens a tendenc to knock. Any extension of the high pressure port 35towards the chamber at full mesh lies radially inside of the path oftooth contact li. The end oi the port Ma may extend to the contactclosing point 23 (or slightly beyond for the overlap). The ports [4 andiii in Fig. I are for reversible operation,

extending to 47 and 48 respectively, corresponding to theextension M inFig. VI and the end of the port Ala without the extension 32, the points28 and 29 in Fig. I being the same points in Fig.

In Fig. V the chamber between the points 33 and 26 is about to connectwith the crescent space between 26 and 260. where low pressure prevails,so it has to disconnect (except for the overlap) from the high pressureport 36. long low pressure port in Fig. V, including the crescent spacefavors high speed of operation. The abutment for these five to seventooth rotors is shown in this figure, its outer boundary extendin fromthe end 3! of the port 36, along the lower side of the outer rotor toothin this rotor position, to the path of contact ll, up along the path tothe contact 33, thence along the lower edge of the pinion tooth to theinner boundary 29 of the port 36. The outer boundary may be circulararound the outer tips of the tooth spaces.

If the chamber has reached its limit of: closing it has reached a pointwhere it is ready It provides a leak from the 1 The These outlines maybe modified as already described. They are adapted to high pressureoperation.

Owing to the need of precision here and there, the wide lines ofdrawings are representative only.

Liquid pumps In our pinion drive liquid pump, the drive shaft isconnected to drive the pinion. The low presat 13c and Nil).

sure intake ports in Figs. I, V and, VI are I3, 36, and 35 respectivelywhen operated anticlockwise (see arrows in Figs. V and VI). Chambersalong the other high pressure discharge ports are subject to anopeningforce opposing the driving force on the shaft, which causes theteeth to make driving contacts and pressure holding engagements betweenopening chambers. Overlap of ports is useful to minimize cavitationnoise. It may be accomplished by difierent modifications of ports, amongwhich are shown the chopped-off portions of the abutment 34 one or both,Fig. V, and 34a and 5| in Fig. I, at the two ends 40. The mass andmomentum of the liquid operate to prevent any substantial leakage whenthe overlap is correctly proportioned. The overlaps at 4% may be variedto accommodate the speed at which the mechanism is to run,a very smalloverlap doing for low speed and a much larger overlap for high speed.This overlap also may be accomplished by shifting the two sides of theabutment a little closer to each other or similar shifting of othercontours of the ports. This overlap is not a necessity in all cases inthe hydraulic motor, pinion drive, described above.

Reversibility rated from a neutral port area d9 by abutments at 340. and5|, similar to the abutment 34 in Fig. V. If the pinion in a pump withback lash drives the outer rotor, shown in broken lines, clockwise, thedrive engages the teeth of the opening chambers, so that only the teethforming the opening chambers are kept tight b the driving relation. Theteeth, with their back lash, between the closing chambers are. thereforenot tight, and fluid pressure in the outlet port is transmitted betweenthe teeth to the neutral port area 49. -The abutment 5! is the one thatprevents pressure from the port l3 from flooding into the intake port14.

That the neutral areais not required to be separate in all units isindicated in Fig. VI. In

low pressure pumps and low speed pumps, or other fluid mechanisms, theneutral port is of lesser consequence.

The ports have another feature of importance. It may be noted that withrotors having a difference of two teeth, the ports are shorter than withrotors having a difference ofone tooth, but they are wider radially.Rotor chambers have greater displacement volume. More port area may beadded on the opposite side of'the rotors as indicated in Fig. II, whereport is is shown This doubles the already enlarged port area, allowingfree intake of low pressure liquid, drawn in by suction (popularlyspeaking). These ports communicate with piping passages 52 and 53.Having the same fluid But the port extensions 32 and 44 are no longerpermisare equal.

pressures on both sides, rotors do not of themselves tend to pressagainst either front or rear .wall and so create wear.

Bearings In the ordinary pump art it is customary to allow up to seventhousandths of an inch clearance in the journal per inch of shaftdiameter. It is evident that if rotor contacts are as loose as that,they could not exert the continuous "liquid pressure holding engagementsintended.

and prevent binding.

Radial pressures on the bearings may be opposed by fluid pressures inthe bearings having the same pressure as in the rotor chamberscounteracting the load pressure upon the bearings. This mechanism isadapted to be cast, die cast or plastic molded, so that the liquidpressure balancing system is designed to permit withdrawal of formingmembers of molds from casing members containing the bearings. Liquid balancing is accomplished preferably by grooves parallel to the rotor axes,around the outer rotor and around the shaft carrying the pinion. Thesegroo es are grouped in zones 59 and 50; opposing pressures, high or low,in the ports 45, i3 and Hi respectively, so that whatever the fluidpressure in any port area may be it is instantly communicated to thezone of grooves that will oppose the pressure in the port androtorchambers connected to it. The grooves are connected together, at theiropen ends by circular recesses so that the pressure in the grooves ofany zone These recesses are capable of being molded, and with a pressmember capable oi being withdrawn after molding. Circular ductsimpressed upon the end face of the casing member, indicated in Fig. IIIfurnish the means of making these various interconnections for thegrooves around the shaft bearing in the casing member l2. The circularduct 82 is connected to the zone and its recess, 58, as indicated and bya hole 63 thru the casing 2 to the port 49. The duct E l, connected bythe hole 85 to port i3, is connected to the zone 59 by holes 66 drilledas indicated in Fig. XIV, until they meet. The duct 61, connected by thehole 58, to the port M, is connected to the zone 60 by holes similar to5 8 in Fig. mV, as shown at 59 in Fig. XV. Thus each port, intake,outlet and neutral has its zone of opposing pressures, regardless ofwhat the pressure may be under the conditions of operation heretoforedescribed. The various ducts are closed by the gasket 10 clamped to thesurface by means of the screw seal cap H. The zones or recesses at theends of the bearing grooves are closed by the plate 12 pressed againstthe casing member 'H by the spring 18. The seal cap may contain theBeach seal comprising a sponge rubber or neoprene sleeve 13 clingingtightly to the driving shaft is journalled within the zones 58, 59 and0d, and additional zones at its other end to be described later. Uponboth ends of this sleeve 13 are mounted caps 75 and '16 free to move ason a universal joint and thus to always lie flat against an end sealplate H,

and the thrust plate '72. The rubber may-exert presture thru the sealcaps against these end plates; assisted, for higher pressure or vacuumservice, by a helical spring 18. The rubber sleeve, caps and springrotate with the shaft. The caps may be of a special plastic or Bakelite,and the thrust plates 12 and ll of bronze. The-special plastic is athermosetting compound of resin, fibre and graphite. The space aroundthe 'rotating seal members is connected to a low pressure port in eachpump for best service, as by a duct '19, Figs. II and III.

The right end of the shaft, 73a, is similarly mounted in a bearing inthe cover member of the casing, the bearing having similar grooves,recesses and zones as the other end of the shaft. The ZOIlfS and portsare interconnected by ducts in the cover member. They are alsoillustrated in Fig. XVI. Around the outside edge of the cover is theduct 8| connected to the Zone 5911 by the hole 32 and by the slot 83,Figs. II and XVI, to the port area {3b. On the outer face of the coveris the duct 8% connected to zone 60a by the hole 35, and to port M by ahole 35. Another duct 8'! connected to the zone 580; by the hole" 88, isconnected to the neutral port by a hole '89. Thus connected these zonesreinforce the zones at the left end of the shaft and together in areashould balance as near as may be, the pressures in the rotor chambersand the ports connected to them. In 5 and 7 tooth rotors there'is avariation of pressure of some 40%. But rotating parts have momentum andinertia, and an average balance for usual motor speeds accomplishesexcellent results. The balancing pressures counteract the shaftpressures on solid bearing walls, reducing both Wear and friction.

The space at the right end of the shaft, .at .90, Fig. II, is connectedto the low pressure area in each type of mechanism as by a slot at 9!.

The open ends of the grooves and recesses 58a, 53a and 50a are sealed bythe ring 92, adrive fit in the cover member and freely fitted to theshaft. The cover member 89 is fitted to the casing i2 and against ashoulder 93 to provide correctrunning clearance for the rotors 42 and96. A gasket 9 covers the ducts 8t and Bi, and both cover and gasketheld tightly against the casing shoulder 93 by the hollow nut 85. Thethreadsof this screw joint are loose enough to let the screw adjustitself to the cover and shoulder. To enable the teeth 9*5 of the pinionrotor, integral with the shaft M. to find their easy running positionbetween the cover 80 and the back wall in the casing 12, the shaft hassufficient freedom endwise. To avoid interference from outside thrustsan Oldham clutch is employed, illustrated in Figs. II, VII, and XVII.Lugs 97 and 98, at right angles to each other, on the shaft ends, engagerecesses in a middle disc member 99, Fig. VII, with allowance for radialand endwise freedom to accommodate axes not always in perfect alignment.In case the shaft M is molded plastic, the lugs 98 are on a metal cappiece shown in Fig. II having a rough interior to grip the plastic,during molding at 375 F. and under 5,000 lbs. p. s. 1. pressure.

Ratios Our invention is applicable as to some of its features to manycon-tant contact ratios. The 5 x 7 ratio is unique in that it has thefewest permissible teeth of the basic fractional ratios for general use,its displacement for high pressures requiring a driving shaft so largethat the teeth pinion tooth at full mesh in Fig. VIII with enough of themiddle of the tooth, as between broken lines IZI, removed to add anothertooth to each rotor, the outer teeth being correspondingly narrowed. InFig. XI the complete tooth curve I! is generative of the dominating ormaster curve lllla which may or may not be circular. A part of thistooth curve may be employed to form the tooth 102, its other side beingthe same curve in reverse, or some other curve adapted to acorresponding other curve on the teeth of the outer rotor. These toothforms, and their pressure angles may be improved by redesigning inaccordance with the system of designing rotor con"- tours illustrated inFigs. XII and XIII.

Our earliest efiorts in rotors, indicated in Patents 1,682,563-4-5, werebased upon the hypo system of generation, where a pinion tooth form,preferably circular, was used as the master form by means of which therotor contours were designed by generation. The shortcomings of suchrotors were expensive. They were remedied by a reversal of the method,so that a master form was the tooth form of the outer rotor, stillpreferably circular and the outer rotor tooth spaces were narrow. Themain advantage of the cicular form is the comparative ease of makingtools, since other forms require special and intricate mechanicalequipment. The narrow tooth spaces in the outer rotor help to eliminateliquid jamming at full mesh.

New geometry Figs. XII and XIII illustrate the method of designingcomparative rotor contours. The ratio of the rotors having five to seventeeth is 'used to design diiferent circroids and corresponding rotorcontours, to estimate their relative values. They comprise an outerratio circle Bor arcs of it having a radius 3 times the eccentricity(see pc to ac, Fig. IV), a pinion ratio circle A having a radius 2%times the eccentricity (pc to ac, Fig. IV), a radicroid R, that is, aradius of the outer ratio circle, extended to a circroid at a chosendistance which may be varied for varying the circroid, and positionsalong a cycloid which assistin locating the radicroid in successiverolling positions, that is, rolling of an outer ratio circle upon thepinion ratio circle as its outer tip traces a circroid. Fig. XIIutilizes the pinion ratio circle and the circroid to explain thecritical factor that determines the inner limits of the pinion contour,generated by a selected form fixed to the end of the radicroid R. Acircular form is usually employed, but other forms may be used.

. In Fig. IGII the pinion ratio circle A is divided into an equal numberof arcs. Ten are convenient for a five tooth pinion, starting from theradicroid position R, some of which are marked 00, 11, 22, 33, 44, 55,66, and 77. An extra division between 22 and 33 assists accuracy forreasons to follow. It is marked 25. An eccentricity. circle E isdescribed from the center Y of the circle A, with a radius equal to theeccen-. tricity for the proposed rotor curve. This circle is alsodivided into ten parts, 0, l, 2, 3, 4, 5, 6, and 7, etc. The otherpoints are not used. The starting position of the radicroid is from thepoint 0 in E thru the point 00in A, and on out to the point 000 selectedas an experiment. The

- ratio circle of the outer rotor is not drawn in full to saveunnecessary confusion, and is indicated by the arc B in the startingposition. As the ratio circle B rolls on A it assumes successivepositions indicated in broken lines Bi, B2, B3, B4, B5, B6, and BI. Asthe ratio circle rolls, and assumes the various positions BI, B2, etc.,a point 00 travels along the cycloid thru the various points 10, 20, 25,30, 40, 50, 60 and 70, sincea point in one circle rolling on anothertravels along a cycloid. Meanwhile the cente of this ratio circle, point0 in the circle of eccentricity E, travels around this circle E thru thevarious points 1, 2, etc. to swing the radicroid. As the radicroid Rcoincides withxand includes the radius of B, and moves with it, its tip,out beyond the ratio circle, traces a curve, which runs thru the points000, 100, 200, 250, 300, 400, 500, 600, 700, etc., or as many others inbetween as may be needed for accuracy. This is the circroid wanted fortrying out rotor curves. Another might be C I.

length of the radius of this master generating circular arc Ml. If it istoo long, a critical portion of the envelope T will be broken into partscrossing some normals at different angles. There must be a criticalpoint outside of which the perfect rotor tooth contour must lie. If itis to be parallel to the circroid it must have all its normalsi. e.normals to its tangents-also normal to the envelope, and for anequidistance envelope all such normals must be of equal length. If thecurve Ml should be changed in curvature to a non-circular curve, theenvelope corresponds to its irregularity. But in that direction liecomplex tooth forms with circroidal additions to correspond. I

Just as a radius of a circle is normal to it, so circroids for circularcurves have radii normal to them. They illustrate the principle involvedto better advantage. Such radii are the instant lines from given pointsof the circroid to corresponding points on the ratio circle A to whichthe ratio circle B is tangent during its rotation. The end of theradicroid, while tracing the circroid, is swingingor turning on atravelling point the point of tangency between the circle A and B. Theseinstant radii are indicated, or a few of them are indicated in this Fig.XII, one from 200 to 22, and another from 300 to 33. They converge morethan any of the other lines from other points. Another line from 250 to25 also converges toward 300 to 33, even more. That point ofintersection between these various instant radii nearest to thecircroid, is the critical point that We are after, since any envelopebeyond it is broken up by arcs lying at interfering angles. This pointof intersection is indicated at N. An envelope between N and thecircroid 0 described by any curve Ml will provide a tooth curve having acontinuous contact relation with an outer rotor tooth having that curve.

The distance of the tip oi the radicroid to its ratio circle is termedthe circroidal addition," and with a given ratio, this circroidaladdition determines the distance of N from it. Circular master formshave been described, but any tooth curve designed for rotors or gearshaving radii of curvature greater than zero where it crosses the ratiocircle, must observe the requirement of the circroidal addition in orderto maintain continuous fluid pressure holding contacts at steady speed.(The same is true as to such tooth curves cut off at the ratio circle asin certain gears.)

The nearer the tip of the radicroid is to its ratio circle, the lesserthe radius M. By such reductions the instant, radii of the circroid arereduced. If this reduction is carried to its limit zeroethe circroid ismerged into a cycloid as L in Fig. XIII, and the radius of MI iscorrespondingly reduced to zero. To put it another way, there is noenvelope possible within a cycloid and equi-distant from it. It is thefailure of gear designers generally tounderstand this fact that isresponsible for noisy gears and limited durability.

One would naturally suppose that in order to generate a tooth of a rotoror gear, a blank would be located on the inner ratio circle axis, and atool to generate with, located onthe outer ratio circle radius and thatgeneration would produce continuous contact tooth curves When thisprocess failed, as it always must, to produce the smooth acting curve,it was a puzzle. The generating tool, one would argue, certainly couldnot be carried on a greater radius than that of the ratio circle,because the speed ratio would be changed. That is where efforts to solvethis rotary problem undoubtedly stopped. It is the. il-- logical ideathat solved the enigma. While a master form is mounted on a radicroid ofgreater length than the radius of a ratio circle, nevertheless theresulting generated tooth contour may lie across the inner ratio circleas gear teeth should, and thus travel at thespeed ratio. It also mightlie outside of the ratio circle with continuous tooth contactsv but thatlocation introduces angular slip and poorer pressure angles, Circulartype rotor contours may have more than one circroidal addition if mergedinto each other. If a master form is a composite of different radii ofcurvature, the point N is to be determined from the several segmentswhich lie nearest to the nearest circroid. Contours once determined maybe modified where not needed for engagements.

In order to locate as accurately as possible, the intersection N in Fig.XII a large chart was used, and instruments of accuracy located thevarious points involved. The relative location shown is approximate. Anumber of normals were drawn from points on the circroid between 200 and300 to corresponding points upon the ratio circle A before the point Nwas finally located. Varying the ratio or circroidal addition shifts thepoint N. It must always be theintersection that is nearest to thecircroid. For the relations shown in Fig. XII the intersecting normalsor instant radii of the circroid are between the 200 and 300 positions.For other relations it is nearer the point 000 or further away from it.Some of the normals diverge and requirenoconsideration. The intersectionmight be considered to be an apex of a triangle whose base is betweentwo points on the circroid at an infinitely small distance from eachother, and sides converging at an infinitely small angle. While thediagram method is a shorter and easier one, differential 20 equationsmay be used to. find the mathematically correct N. The idea that agenerating tool should be centered upon a rolling circle larger than aratio circle appeared impossible for producingteeth of the correctratio. In effect our invention altered the speed of thislarger-than-a-ratiocircle to compensate for its disproportionate size.

Practically, the tooth curve is drawn as an envelope outlined by arcsMl, M2 etc. having a, radius of M and centered at successive points allalong the circroid. The radiusv M must locate, the envelope between thepoint N and the circroid. The nearer this envelope isv to the circroid,the more it partakes of its curvatures. The nearer it is to the point Nthe sharper the curvature around N. If carried to its limit, a corneraround N is arrived at, too sharp for use. By having the curve located aslight distance from, N the best results are attained. Also it allows.forminor drafting errors.

Pressure angles are involved in the radius. of the curve MI. The lessthe radius, the greater the variationin the pressure angles inthedriving range. The best average pressure angles for a given ratio arederived from the largest useful radius of curvature. The inclination ofthecurve is also better with a larger radius, due to the curve centersbeing so much farther. away around the ratio circle, as indicatedinFig,.,XII where 000 is far to the right of the vertical axis, while,the. toothcurve Mi is far to the left- The pressure angle is equal tothat between atangentto the driving curve at any point, and a radius ofav ratiov circle to that point. During a driving relation, over adriving range of one tooth division, the tangent point is travelling,hence its angl'evaries. A fixed pressure angle bars continuous toothcontact in the driving range.

As the circroidal addition is reduced as derscribed, the critical normalfrom thecircroid; to, the ratio circle is ever shifting along thecircroid towards 000. With changes in the numbers of teeth, and withvariations of the other factors mentioned, the location of the normalalso changes in one direction or another, and in designingdifferentrotors, with different relativeradii of curvature; these various changesarestudied to select the forms most suitable for the rotors desired,compromising upon numbers of teeth, size of master curves,circroidaladditions, for strength, low-pressureangles, and displacement. By making graphs of the effect of the changes of each of thefactors, one is enabled to select more intelligently the form bestsuited to the problem in hand.

In Fig. X is illustrated a comparison between the displacement of 6 and'7 tooth rotors at I50; and l6a'and5' and 7 tooth rotors at I51) andI6b;. the former being in broken lines. The great difference indisplacements is evident.

The rotors in Fig. IX, tho having a difierent ratio have the teeth ofthee and 5 tooth form (hence of greater displacement than- 6 x 7 rotors)indicated in Fig. VIII, omitting half of the teeth andtooth spaces.After doubling these numbers 4 and- 5, the ratio circles-were reduced bysubtracting three from both numbers to the 5 and? ratio, and the teethdisposed accordingly. The design in Fig. X, in full lines resulted fromthe geometrical studies in Figs. XII'and- XIII. The pinion shaftdiameter is the same in both figures. In Fig. X the rotorchambersreach-the shaft almost, while in Fig. IXthe chambers-areshallower. The pinion teeth in Fig, IX have thesame tops as those inFig.'VIII, losing that'extra depth 21 of rotor chambers gained partlyby'bring'ing the sides of a pinion tooth closer together. In our gearPatent 2,091,317 the type of tooth corre- 'sponds to Fig. IX, but of adifferent ratio, not with odd numbers of teeth but with even numbers ofteeth (which lose the hunting relation) between all the teeth. The teethof the rotors in Fig. XI, 9 and 11 in ratio, have deeper rotor chambersand the full hunting relation. p

In order to design these 9 and 11 tooth rotors the ratio circle A ofFig. XIII has a radius 4 times the eccentricity, and the ratio circle Bhas a radius of 5 /2 times the eccentricity. Circle A has a number ofdivisions laid off on it of equal length and the points of the cycloid Lare located to accord with them. The rest of the procedure is similar tothat for the 5 and '7 tooth rotors, except that the radius M and thecircroidal addition have to be experimented with to get the best form oftooth curve, the best pressure angles, sufficient tooth size andgreatest displacement for the different ratio. sists of varying thecircroidal addition by varying the extension of the radicroid beyond'itsratio circle, then finding the point N for such circroid as may bedescribed by the radicroid, and then with a radius a little short of thepoint N, outlining a rotor tooth curve.

After describing a curve that appears satisfactory for the tooth ratio,its driving relation, its displacement, its pressure angles, etc., thenext step is to select the portion of such a tooth curve desired for arotor tooth for a five tooth pinion. The curve T may be one side of atooth. Obviously half a tooth is limited to one fifth of 360 divided by2, which is 36. So next it is desired to find out what part of the curveT may be utilized for one half of the tooth. The broken lines GY and HYare drawn from the ratio circle center Y at such an angle of 36. Byswinging them around the center, back and forth, keeping theirangularity to each other fixed they include different portions of thecurve T. The partincluded in this figure is from G to 1-1. If swung tothe right, the end H is nearer the center Y, and there is little changeof diameter at G. This might be desirable as it increases displacement,but for many uses the shaft usable with this contour would be too small.Also the teeth might lack strength as being too thin. The teeth shown inFigs. IV, V and VI show the final compromise between these factors. Theywould have to be integral with the shaft for purposes of strength, aunique case. Smaller ,ratios usually need outside gears to drive them.The next larger .ratio having the desirable hunting relation is the 7and 9 ratio. The next, the Q and ll ratio. The first three ratios morethan cover the ground of the Gerotors now in use having ratios of 4 and5, 6 and 7, 8 and 9, and 10 and 11; so that the new rotors cut the rangeof manufacturing equipment down to 75% of that required for the olderform. Furthermore, the 5 and 7 tooth ratio supplants both the popular 4and 5 tooth, and the 6 and 7 tooth rotors-for many uses.

Another popular size of rotors having eight and nine teeth is 1% inchesin diameter, the same size as the rotors shown in Fig. XVIII, at

Such experimentation con-.

Md and 32d. These rotors have 11 and 13 teeth, and have a greaterdisplacement than the 8x 9 rotors, thereby reducing friction andincreasing pressure capacities, as well as delivering a steadier' flowof fluid. Rotors of this size are :useful in oil burner pumps, and insupercharger, scavenging and lubricating pumps (double) of superiorservice for high altitude flying on account of their high suctioncharacteristics. Ports are designed in accordance with the conditionsand limitations described with relation to Figs. I, V, and VI, etc.',with port areas inside and outside of the path of tooth engagement. Thepipe connections to the ports are threaded as shown at |03.- The pinionis separate from the shaft if desired, in which case it is keyed as atI04. The section in Fig. XVII shows the same balancing of fluidpressures, the ducts, etc. as shownin Fig. II, the connections followingthe method shown in Figs. III, XIV, XV and XVI; with the exception thatthe nut Hi5 replaces the seal cap ll in Fig. II. The screw cap Hi6 holdsthe seal thrust plate it? in position. Between the thrust plates 161 andH38 in'the casing, is located the seal. It'may be combined with theclutch disc I09 shown in larger size in Fig. XX. As shown in Fig. XVIIthere is endwise freedom between the shafts I H and H2 so that thrustmoments on the shaft H2, as when it is a motor shaft, will not put acorresponding thrust on the pinion lill against the casing wall.

It hasbeen the custom, as shown in Fig. II, to put a sponge rubbersleeve 53 on the shaft M, which is supposed to rotate with the shaft. Ifneoprene is substituted in order to pump oil (rubber being softened toimpotence in oil) the neoprene slips on the shaft and does not rotatewithit. Soon leakage develops. Therefore we prefer to make a unionbetween the sleeve and the rotating memberthe Oldham clutch disc such asby vulcanization, there being a fixed ring or band I 13 between the discand the sponge rubber or neoprene ring I I4, vulcanized or cemented toboth. The object of this sponge rubber, neoprene, or other resilientsubstance is to prevent idiosyncracies of the disc from beingcommunicated to the seal caps I I5 and I I6 mounted and vulcanized tothe rubber, etc. These maybe of stainless steel or bronze, spaced apartand pressed against the thrust plates 59'! andlOB by a spring Ill, whichfor convenience may be a spring washer of hardened stainless springsteel, crimped into a wavy form indicated in Fig. XIX, hich shows asection of it. The strength of the 3 spring is adjusted to resistseparation of the bronze shoes from the thrust plates. Without thisrubber, a disc corresponding to E09, once tried in the 8 x 9 toothedrotor mechanisms,

leaked. Therecesses in the disc indicated by broken lines, fit the lugsI I3 and H9 allowing radial freedom, and have the same shape as in Fig.VII exceptthat the diameter is larger as vindicated in Fig. XIX, andadapted to fit the ring H3.

The form of casing members in Figs. XVII and II permits them to bemolded from the special plastic composed of graphite with strengthfibres thru it with a thermoset resin. This powder does not easily flowin transfer molds and is made of biscuits, preformed cold from powderwith mild pressure; which in the molds under some 5,000 lbs. p. s'. i.and at a temperature of around 375 F. becomes a strong structure withvery slight coefiicients of expansion; and impervious, to water, oil,and most acids. It may be cooled in the molds before removing pressure.Theaccuracy possible makes machining unnecessary. The casing members areeach molded in a mold to form their exteriors, with rains to form theinteriors including port areas. The casing members 1 instead of beingboltedl together are, united by hollow nuts which bin'dthe covers (Fig.II) "and various needs.

1 {9 (Fig. XVII) against-gasketsfl and H1 (Fig. II) and IZO'andI-2i(Fig. XVII) which are thus bound tight against shoulders in thecasingmembers respectively. The gasketsmay beof rubber and fabric withslight compressibility to'equalize of plastic, it is molded into adriving cap having the lugs 98. The inside ofthe cap is knurled orroughened for a secure grip onzthe plastic material. If its coeflicientof expansion is greater than that of the plastic, as it cools it gripsthe plastic ever tighter.

There .is no limit'theoreti'cally to the highest numbers of teethpossible with-.our ratios having a difference of two or. more teeth. Theleast number of teeth is determined by the manner of driving relationthat keeps them running .;at the steady ratio speeds necessary forcontinuous fluidtight engagements. Aratio of.5.x 7 teeth provides anexcellent driving relation between the teeth, far better than with teethhaving commercial forms now generally used outside of the Gerotor art. Aratio of3 x 5 is possible, particular-ly for an oil pump due to thelong. driving con- "tactacross full mesh of a rolling character.Howeverit has to be assisted in part of the driving range by a veryconsiderable radial rubbing action between the teeth. With the plasticor other durable materialfor the tooth surfaces even this rubbing actionis not prohibitive. -With rotors having 1 x 3 teeth however outsidegearing may be used to keep 'them in notvery :accurate-regis 'tration,but enough so to *do some pumping or blowing of air or gas, as well asliquid. Other low ratios doubled, trebled or multipled may fit All thesemodifications lie within the scope of our invention.

The importance of continuous engagement at steady'ratio speed is-perhapsrealized in connection'with such low ratio rotors-where continuouscontact means one contact, not two-or three, and its continuity meansnothing if tooth curves are irregular, since the teeth might haveunsteady speeds and still maintain some continuouscontact. 'Onlycorrectcontours based on the circroidal addition make possible steadyratiospeeds.

Other master generating. contours 'suchas oycloids, ellipses, ovalcurves or a series of one or more of them and mated contours of them,are useless unless subject to our correct circroidal addition, hence,made operable by "the light thrown on the problem by our invention.

In operation as a pump, a shaft 14 '(Fig; '11) driven by an outsidesource of power'applied tln'u an Oldham clutch 9T, 93, v99 turnsithepinion or displacement member 96 which in turn drives the teeth of theouter rotor displacement "member 42 where the rotor chambers areopening. The

' driving action of the shaft and the resistance of the outer rotor dueto high pressurein-the closing chambers (which vtends to ;open;themby-reverse rotation) exerts an opposing force ;that keeps the contactsand pressure holdingengagements between the driving teethtight. "Theclosing chambers are connected'to' eachpther and to the crescent. spacethrough backlash between the teetn but p essu e is un l to pass the teeh c n ac ndabutment-a e endjo t e at s space nearest the intake port.

When .operating .as a hydraulic motor, ,in the reverse direction,pressure .fluids enter thru the same high -pressure port, expand thechambers and cause rotationin ,a reversedirection to that of -,a;pump.'Pressureliquids impel the rotors in the reverse direction, but thepinion driving shaft, carrying a load resists so that the outer rotorruns ahead of the pinion to the extent of the backlash, andis thenstopped byengaging closing teeth of the: pinion, thusassisting inmaintaining rotation. These pressure holding toothengagements preventliquid from forcing its way thru .the device exceptaspermitted byrotation.

.The foregoing description explains the various features of ourinvention and difierentiates it .fromthe-prior art. The novel featuresand functionslie within the suspect our invention.

What we. claim is:

1. In va rotary fluid mechanism, a casing, toothed displacement rotormembers in said casingyone rotor member within and eccentric to theother, one ,rotor member having inwardly projecting teeth and the otherrotor member having outwardly projecting teeth meshing therewith, saidteeth having contours providing a crescent space between the teeth whereno tooth engagement occurs, saidtooth contours providing for continuous,drive contacts and fluid pressure holding engagements, along a path ofcontact between full n1esh and saidcrescent space where needed for theperformance of fluid pres sure functions,..while traveling at steadyratio speeds, drive. means for said rotary displacement membersproviding-for saidvdrive contacts and .said pressure holding engagementsalong a path ofcontact, said tooth. contours providing rotor chambersbetween said teeth which open and ..close during. rotation; high .,andlow pressure ports in :saidcasing located along said path, a

port communicating.withopening chambers and a .port communicatingwithclosing chambers, abutment areas located. ona said .path between saidports to check leakage from'a high pressure port to a low pressure port,said-abutment areas located to provide an interval between them forfluid displacement insaid rotor. chambers, said tooth contacts andengagements cooperatingwith said abutment areas in sealing said portsfrom each other, said tooth contours being located around ratiocirclesor curves and including centers of curvature traveling far enoughoutside of said ratio circles or curves to provide said-con-"tinuouscontacts and engagements, the numbers of-teeth of said twodisplacement rotor members difiering by two or-more and having a basicfractional ratio differing by one.

2.-The combination claimed in claim -1 having the contours on one sideof the teeth shifted angularly to providebacklash in reversible rotors.1 3. The combination claimed in claim 1 having mainly convex curves onthe crown portions of the teeth of the outer rotor rolling upon themainly concave tooth curves of the inner rotor. L'The combinationclaimedin claim 1 having circular arcs for convex curves on the teeth of onerotor and the other tooth contours of both rotors determined by mutualgeneration.

- 5. The combinationclaimed in claim 1 having one or-more of saidportslocated radially inside and-outside ofsaid paths of contact.

" 6. The combination claimed; in claim 1 having I 25 a ratio of seven,to five teeth on said rotor members, the five teeth on the inner memberbeing integrally united to a supporting and drive shaft, said driveshaft having two sections one within said mechanism and one without withan endwise loose connection between them. 7

7. The combination claimed in claim 1 having a two part drive shaft, oneinside and one outside of said mechanism, loosely united end to endthrough a seal member acting as a seal around said shaft.

8. The combination claimed in claim 1, including a drive shaft, and aseven tooth inner rotor member removably mounted on said shaft.

9. The combination claimed in claim 1 including a drive shaft, and anine tooth inner rotor member removably mounted on said shaft.

10. In a rotary fluid mechanism, a casing, toothed displacement rotormembers in said casing, one rotor member within and eccentric to theother, one rotor member having inwardly projecting teeth and the otherrotor member havin outwardly projecting teeth meshing therewith, saidteeth having contours providing a crescent space between the teeth whereno tooth engagement occurs, and providin back lash between them, saidtooth contours providing for continuous drive contacts and fluidpressure holding engagements where needed for the performance of fluidpressure functions, along paths between full mesh and said crescentspace while traveling at steady ratio speeds, drive means for saidrotary displacement members providing for said drive contacts and saidpressure holding engagements, said tooth contours providing rotorchambers between said teeth opening and closing during rotation, highand low pressure ports in said casing located along said paths, a portcommunicating with opening chambers and a port communicating withclosing chambers, abutment areas between said ports located on a saidpath to check leakage from a high pressure port to a low pressure port,said abutment areas providing an interval between them for fluiddisplacement in said rotor chambers, said tooth contacts and engagementscooperating with said abutment areas in sealing said ports from eachother, said tooth contours being located around ratio circles or curvesand including centers of curvature traveling far enough outside of saidratio circles or curves to provide said continuous contacts andengagements, the numbers of teeth of said two displacement rotor membersdiifering by two or more and having a basic fractional ratio differing:by one.

11. The combination in claim 10 having said crescent space communicatingwith a high or low pressure port, thru back lash. I

12. In a rotary fluid reversible mechanismja casing, tootheddisplacement rotor members in said casing, one rotor member within andeccentric to the other, one rotor member having inwardly projectingteeth and the other rotor member having outwardly projecting teethmeshing therewith said teeth having contours providing a crescent spacebetween the teeth where no tooth engagement occurs, said tooth contoursprovidin for continuous drive contacts and fluid pressure holdingengagements along paths between full mesh and each end of said crescentspace While travelling at steady ratiospeeds', and

. where needed for the performance-,of fluid pressure functions {drivemean for said rotary dis- Y placement members providingfor said drivecons tacts and said pressure holding engagement along either of saidpaths, said contours providing rotor chambers between said teeth openingand closing during rotation; high and low pressure ports in said casinglocated along said paths, a port communicating with opening chambers anda port communicating with closing chambers, abutment areas in saidcasing along said paths between said ports to check leakage from oneport to the other, located between full mesh and each end of a saidcrescent space, said tooth contacts and engagements cooperating withsaid abutment areas in sealin said ports from each other, said abutmentareas located to provide an interval between them along either of saidpaths for fluid displacement in said rotor chambers, while rotating inone direction or the other, said tooth contours being located aroundratio circles or curves and including centers of curvature travellingfar enough outside of said ratio circles or curves to provide saidcontinuous contacts and engagements, the numbers of teeth of said twodisplacement rotor member differing by two or more and having a basicfractional ratio diiiering by one.

13. In a rotary fluid mechanism, a casing, toothed displacement rotorsin said casing, one rotor member within and eccentric to the other, onerotor member having inwardly projecting teeth and the other rotor memberhaving outwardly projecting teeth meshing therewith, said teeth havingcontours providing a crescent space between the teeth where no toothengagement occurs, said tooth contours providing for continuous drivecontacts and fluid pressure holding engagements along paths between fullmesh and said crescent space while travelling at steady Y ratio speeds,and where needed for the performance of the fluid pressure functions,drive means for said rotary displacement members maintaining said drivecontacts and pressure holding engagements, said contours providin rotorchamalong a path of contact between said ports, said abutment areasadjusted in area with relation to said rotor chambers to provideover-lap of said chambers between said ports, said tooth contacts andengagements cooperating with said abutment areas in otherwise sealingsaid ports fromeach other, said tooth contours being 10- cated aroundratio circles or curves and includ- '-'ing* centers of curvaturetravelling far enough outside of said ratio circles or curves to providements occur, said contours providing for continuous drive contacts andfluid pressure holding engagements along paths'between the full'meshregion and-said crescent space where needed for the performance of fluidpressure functions and While travelling at steady ratio speeds, saidcontours providing backv lash between said teeth, drive means connectedto said inner rotor members maintaining said drive contacts and pressureholding engagements along a path of contact, said tooth contoursproviding rotor chambers between said teeth which open and close duringrotation; high and low pressure ports in said casing located along saidpaths, a port communicating with opening chambers and a portcommunicating with closing chambers, abutment areas in said casing alonga said path between said ports to check leakage from a high pressureport to a low pressure port, said abutment areas located to provide aninterval between them for fluid displacement in said rotor chambers,said tooth contacts and engagements cooperating with said abutments insealing said ports from each other, said tooth contours being locatedaround ratio circles or curves and including centers of curvaturetravelling far enough outside of said ratio circles or curves to providesaid continuous contacts and engagements, the numbers of teeth of saidrotor members differing by two or more, and having a basic fractionalratio differing by one.

15. In a rotary fluid mechanism, a casing, toothed displacement rotormembers in said casing, one within, and eccentric to the other, onerotor member having inwardly projecting teeth and the other rotor memberhaving outwardly projecting teeth meshing therewith, said teeth havingcontours providing a crescent space at open mesh where no tooth contactsor engagements occur, said contours providing for continuous drivecontacts and fluid pressure holding engagements along paths of contactbetween full mesh and said crescent space where needed for theperformance of fluid pressure functions while travelling at steady ratiospeeds, a shaft drive means for said rotor members maintaining saiddrive contacts and pressure holding engage- :ments along paths ofcontact between f-ull mesh and said crescent space, said tooth contoursproviding rotor chambers between said teeth which open and close duringrotation, high and low pressure ports in said casing, a portcommunicating with opening chambers and a port communicating withclosing chambers, abutment areas in said casing between said ports alonga said path of contact, said abutment areas providing an intervalbetween them for fluid displacement in said chambers, said toothcontacts and engagements cooperating with said abutments in sealing saidports from each other, said tooth contours being located around ratiocircles or curves and including centers of curvature traveling .farenough outside of said ratio circles or curves to provide saidcontinuous contacts and engagements, the numbers of teeth of said rotormembers differing by two 'or more and having a basic fractional ratiodiffering by one, zones of fluid pressure grooves in saidcasing-surrounding said shaft balancing radial fluid pressures in saidrotor chambers on said shaft, a zone for high pressure connected to saidhigh pressure port, and a zone for low pressure connected to said lowpressure port.

16. In a rotary fluid mechanism, a casing, toothed displacement rotormembers in said casing, one within, and eccentric to the other, onerotor member having inwardly projecting teeth and :the other rotormember having outwardly projecting teeth meshing therewith, said teethhaving contours providing a crescent space at open mesh where no toothcontacts or engage:

ments occur, said contours providing for continuous drive contacts andfluid pressure holding engagements along paths of contact between fullmesh and said crescent space where needed for the performance of fluidpressure functions, while traveling at steady ratio speeds, saidcontours providing back lash between said teeth, drive means for saidrotor members maintaining said drive contacts and pressure holdingengagements, said tooth contours providing rotor chambers between saidteeth which open and close during rotation; high and low pressure portsin said casing located along said paths, a port communieating withopening chambers, and a port communicating with closing chambers,abutment areas in said casing along said paths between said ports, saidabutment areas providing an interval between them for fluid displacementin said rotor chambers, said tooth-contacts and engagements cooperatingwith said abutment areas in sealing said ports from each other, saidtooth contours being located around ratio circles or curves andincluding centers of curvature traveling far enough outside of saidratio circles or curves to provide said continuous contacts andengagements, the numbers of teeth of said rotor members differing by twoor more and having a basic fractional ratio differing by one, a shaftfor said driving means, fluid pressure zones along said shaft oppositeto said ports balancing port fluid pressures, a zone connected to saidhigh pressure port, a zone connected to said low pressure port; and athird zone connected to said crescent space providing automatic fluidbalancing pressures in said zone for different fluid pressures in saidcrescent space.

17. In a rotary fluid mechanism, a casing, toothed displacement rotormembers in said casing, one rotor member within and eccentric to theother, one rotor member having inwardly projecting teeth and the otherrotor member having outwardly projecting teeth meshing therewith, saidteeth having contours providing a crescent space between the teeth whereno tooth engagement occurs, said contours providing for continuous drivecontacts and fluid pressure holding en-' gagements along paths ofcontact between full mesh and said crescent space while travelling atsteady ratio speeds, drive means for said rotary displacement membersmaintaining said drive contacts and said pressure holding engagements,

said tooth contours providing rotor chambers between said teethwhich-open and close during rotation; high and low pressure ports insaid casing, a port communicating with opening chambers and a portcommunicating with closing chambers, abutment areas in saidcasinglocated along a said path of contact between said ports, said areasproviding an interval between them for fluid displacement in saidchambers, said tooth contacts and engagements cooperating with saidabutment areas in sealing said ports from each other, said toothcontours being located around ratio circles or curves and includingcenters of curvature travelling far enough outside of said ratio circlesor curves to provide said continuous contacts and engagements, thenumbers of teeth of said two displacement rotor members differing by twoor more and having a basic fractional ratio differing by one, one sideof the teeth of a said displacement member being relieved or cut away toprovidezback lash.

18. In a reversible rotary fluid mechanism, a

casing, toothed displacement rotor members in said casing, one rotormember within and eccen- 29 tric to the other, one rotor member havinginwardly projecting teeth and the other rotor memher having outwardlyprojecting teeth meshing therewith, said teeth having contours providinga. crescent space between the teeth where no tooth engagement occurs,said contours providing for continuous drive contacts and fiuid pressureholding engagements along paths of contact between full mesh and the twoends of, said crescent space where needed for the performance of fluidpressure functions, while travellingat steady ratio speeds, drive meansfor said rotary displacement members providing said drive contacts andsaid pressure holding engagements along said paths of contact; saidcontours providing rotor chambers between said teeth which-open andclose during rotation; high and low pressure ports in said casing, aport communicating with opening chambers and a port communicating withclosing chambers, abutment areas in said casing located along said pathsof contact at full mesh and at each end of said crescent space, andproviding intervals between them for fluid displacement in said rotorchambers, said tooth contacts and engagements cooperating with saidabutment areas in sealing said ports from each other, said toothcontours being located around'ratio circles or curves and includingcenters'of curvature travelling far enough outside of said ratio circlesor REFERENCES CITED The following references are of record in the fileof this patent:

UNITED STATES PATENTS Number Name Date Re. 21,316 Hill Aug. 24, 19281,538,328 Holdener May 19, 1925 1,646,615 Furness Oct. 25, 19271,682,563 Hill Aug. 28, 1928 1,682,564 Hill Aug. 28, 1928 1,682,565 HillAug. 28, 1928 1,798,059 Bilgram et al Mar. 24, 1931 1,927,799 Mann Sept.19, 1933 1,972,565 Kempton Sept. 4, 1934 2,031,888 Hill Feb. 25, 19362,091,317 Hill Aug. 31, 1937 2,209,201 Hill July 23, 1940 2,209,202 HillJuly 23, 1940 2,336,479 Graef Dec. 14, 1943 2,386,896 Hill et al Oct.16, 1945 2,389,728 Hill Nov. 27, 1945

